There's no supported way to change system prompts (i.e. as opposed to custom greeting files) - however you can find the prompt in question under \commserver\localize\prompts\enu\g711\CsSystemTransferScript\
There's a PROMPT.INI file there with the full text of all the prompts in that directory so you can find the one(s) you're interested in. You can record updated versions of these prompts to suit your needs.
Be aware, this is not TAC supported and upgrades will wipe out your changes so you'll have to reapply them in the future if you upgrade. Also, never just remove a prompt - the conversation gets very unhappy when you do this - if you want a prompt to not play you need to replace it with a blank version of that prompt.
